Ti-si-c-n piston ring coatings

ABSTRACT

A Ti—Si—C—N coating for a piston ring and a method forming such coating, wherein the deposited coating exhibits a thickness in the range of 10.0 micrometers to 20.0 micrometers and exhibits a coefficient of friction of less than 0.15 and a wear rate of less than 10−10 −6  mm 3 /N/m. The coefficient of friction being measured on a Plint TE77 and the wear rate being measured against an alumina ball of 0.25 inches in diameter at a load of 1 N at 100 rpm in a dry environment. The deposited Ti—Si—C—N coating includes nanocrystalline phases in an amorphous matrix.

FIELD OF INVENTION

The present disclosure is directed to piston ring coatings and to thepreparation of piston ring coatings of Ti—Si—C—N using plasma enhancedmagnetron sputtering techniques.

BACKGROUND

Automobile manufacturers and component makers have been engineeringautomotive components to achieve the gradually increasing CorporateAverage Fuel Economy (CAFE) standards, which target an average fleetfuel consumption of 34.1 MPG by 2016 and 56.2 MPG by 2025. One designinitiative to achieve CAFE standards is the reduction in the coefficientof friction of moving parts. In addition to achieving CAFE standards, areduction in the coefficient of friction may also reduce wear andimprove reliability of moving components.

One such moving part is the piston ring. One or more piston rings arecommonly provided in grooved tracks around the outer perimeter of anengine piston. Where multiple rings are present, the rings may bedesigned to perform different or overlapping functions. For example,piston rings may be designed to seal the combustion chamber to trapcombustion gasses, improving engine efficiency. Piston rings may also bedesigned to aid in heat transfer and manage engine oil in the cylinder.

Piston rings are often formed from a base material of cast iron orrolled carbon steel and may be coated with relatively hard, wearresistant coatings, such as nitride coatings, exhibiting hardness 2 to 4times that of the base materials. Chromium nitride coatings may exhibitrelatively low internal stress allowing for relatively thick coatinglayers. Chromium nitride coating deposition rates are consideredsomewhat favorable for production at deposition rates of approximately 2microns per hour. Titanium nitride coatings have also been examined.However, titanium nitride coatings may exhibit relatively high internalstress compared to chromium nitride coatings.

The coefficient of friction for chromium nitride and titanium nitridecoatings may be in the range of 0.5 to 0.7 in dry sliding as measured bytypical pin-on-disc testing. Reducing the coefficient of friction valuesbetween a piston and cylinder liner wall may reduce overall enginefriction and improve fuel efficiency. However, maintaining relativelyhigh deposition rates, relatively high hardness and relatively high wearresistance is also desirable. Accordingly, a need for providing arelatively hard, wear resistant, and cost effective piston ring coatingexhibiting a relatively lower coefficient of friction still remains.

SUMMARY

An aspect of the present disclosure relates to a method of coatingpiston rings. The piston ring may be placed into a process chamber andgas pressure in the process chamber may be reduced. Inert gas may thenbe supplied to the process chamber and plasma may be generated from theinert gas. The coatings may then be formed by supplying nitrogen gasinto the process chamber at a flow rate of 40 sccm to 60 sccm, supplyinghexamethyldisilazane at a rate of 3 grams per hour to 9 grams per hour,supplying acetylene at a rate of 10 standard cubic centimeters perminute (sccm) to 50 sccm, and sputtering titanium from a magnetrontarget. A Ti—Si—C—N coating is deposited on the piston ring having athickness in the range of 10.0 micrometers to 40.0 micrometers andexhibits a coefficient of friction of less than 0.15, a wear rate ofless than 10×10⁻⁶ mm³/N/m, and a nanohardness in the range of 10.0 GPato 30.0 GPa. The coefficient of friction is measured using the PlintTE77 testing apparatus using a 10 W-30 oil maintained at 35° C. as alubricant, a normal force of 30 N, and a sliding frequency of 5 to 20Hz. The wear rate is measured against an alumina ball of 0.25 inches indiameter at a load of 1 N at 100 rpm in a dry environment, i.e., withoutlubricant. In addition, the Ti—Si—C—N coating includes nanocrystallinephases in an amorphous matrix, wherein the nanocrystalline phasesinclude TiC_(x)N_(y), wherein x is in the range of 0.0 to 1.0 and y isin the range of 1.0 to 0.0.

A further aspect of the present disclosure relates to a coated pistonring. The coated piston ring may include a split ring formed of an ironbased alloy. A Ti—Si—C—N coating deposited on the surface of the pistonring may have a thickness in the range of 10.0 micrometers to 40.0micrometers that exhibits a coefficient of friction of less than 0.4, awear rate of less than 10×10⁻⁶ mm³/N/m, and a nanohardness in the rangeof 10.0 GPa to 30.0 GPa. The coefficient of friction is measured usingthe Plint TE77 testing apparatus using a 10 W-30 oil maintained at 35°C. as a lubricant, a normal force of 30 N, and a sliding frequency of 5to 20 Hz. The wear rate is measured against an alumina ball of 0.25inches in diameter at a load of 1 N at 100 rpm in a dry environment. TheTi—Si—C—N coating includes nanocrystalline phases in an amorphousmatrix, wherein the nanocrystalline phases include TiC_(x)N_(y), whereinx is in the range of 0.0 to 1.0 and y is in the range of 1.0 to 0.0.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of this disclosure, and themanner of attaining them, will become more apparent and betterunderstood by reference to the following description of embodimentsdescribed herein taken in conjunction with the accompanying drawings,wherein:

FIG. 1 illustrates a perspective exploded view of a piston and pistonrings;

FIG. 2 illustrates a schematic of a process chamber;

FIG. 3 illustrates a schematic of a pin-on-disk tribometer;

FIG. 4a illustrates a schematic of the Plint TE77 test;

FIG. 4b illustrates the testing conditions for Plint TE77 testing;

FIG. 5 illustrates an image of a single cylinder Ricardo Hydra gasolineengine;

FIG. 6 illustrates a single cylinder Caterpillar oil test engine;

FIG. 7 is a graph of the measured nanohardness and Young's modulus ofsamples 1 through 7;

FIG. 8 is a graph of the coefficient of friction and wear rate obtainedof samples 1 through 7 measured using the pin-on-disk tribometer;

FIG. 9 is a graph of the effect of acetylene flow rate on thecoefficient of friction and wear rate of sample 8 through 14;

FIG. 10 is a graph illustrating the effect of sample preparationconditions on the coefficient of friction as measured by the Plint TE77tribometer;

FIG. 11 is a graph illustrating the effect of sample preparationconditions on the coefficient of friction as measured by the Plint TE77tribometer;

FIG. 12 is a graph illustrating the effect of sample preparationconditions on the coefficient of friction as measured by the Plint TE77tribometer;

FIG. 13a is a graph illustrating the effect of sample preparationconditions on the composition of the coatings;

FIG. 13b includes XRD patterns illustrating the effect of samplepreparation conditions on the composition of the coatings;

FIG. 14a is a graph illustrating the effect of sample preparationconditions on the composition of the coatings;

FIG. 14b includes XRD patterns illustrating the effect of samplepreparation conditions on the composition of the coatings;

FIG. 15a includes SEM images of nanoindentations on the coatings of,from top to bottom, samples 3, 4, and 5, the scale set forth in thelower left hand corner is 200 μm;

FIG. 15b includes SEM images of the surface of the coatings of, from topto bottom, samples 3, 4, and 5, the scale set forth in the lower lefthand corner is 5 μm;

FIG. 15c includes SEM images of cross-sections of the coatings of, fromtop to bottom, samples 3, 4, and 5, the scale set forth in the lowerleft hand corner is 5 μm;

FIG. 16a includes SEM images of nanoindentations on the coatings of,from top to bottom, samples 8, 11, 12 and 13, the scale set forth in thelower left hand corner is 200 μm;

FIG. 16b includes SEM images of the surface of the coatings of, from topto bottom, samples 8, 11, 12 and 13, the scale set forth in the lowerleft hand corner is 5 μm;

FIG. 16c includes SEM images of cross-sections of the coatings of, fromtop to bottom, samples 8, 11, 12 and 13, the scale set forth in thelower left hand corner is 5 μm;

FIG. 17a includes SEM images of nanoindentations on the coatings of,from top to bottom, samples 15, 16, and 17, the scale set forth in thelower left hand corner is 200 μm;

FIG. 17b includes SEM images of the surface of the coatings of, from topto bottom, samples 15, 16, and 17, the scale set forth in the lower lefthand corner is 5 μm;

FIG. 17c includes SEM images of cross-sections of the coatings of, fromtop to bottom, samples 15, 16, and 17, the scale set forth in the lowerleft hand corner is 5 μm;

FIG. 18a is a TEM image of a cross-section of the Ti—Si—C—N coating;

FIG. 18b is an SAED pattern of the Ti—Si—C—N nanocomposite coating;

FIG. 19a is a photograph of coated rings, coated according to theconditions of samples 11 and 16;

FIG. 19b illustrates a 3D graph of the topography of a section of thetop ring generated with a 3D microscope after running the engine for 24hours;

FIG. 19c is a profile of the coating taken in the x-direction generatedwith a 3D a microscope after running the engine for 24 hours;

FIG. 19d is a profile taken in the y-direction generated with a 3Dmicroscope after running the engine for 24 hours;

FIG. 20 is a graph of the absolute magnitude of the friction in oneengine cycle for coated and uncoated piston rings;

FIG. 21a is a schematic of the 12 points around a combustion cylinderliner used to take the 12 point step measurements;

FIG. 21b is a graph of the liner wear versus the clock position aroundthe combustion cylinder at which the wear was measured;

FIG. 21c illustrates the measurements of average liner wear of all 12liner wear steps;

FIG. 22a illustrates the amount of iron measured by inductively coupledplasma analysis in engine oil for both coated and baseline piston rings;and

FIG. 22b illustrates the amount of titanium measured by inductivelycoupled plasma analysis in engine oil for both coated and baselinepiston rings.

DETAILED DESCRIPTION

Piston rings are commonly used to provide a seal between a piston andthe cylinder liner so that the engine combustion chamber can achieve adesired pressure. As illustrated in FIG. 1, one or more piston rings102, 104, 106, 108, 110 may be provided around the outer perimeter of anengine piston 100 and are often held in grooved tracks 112, 114, 116formed in the surface 120 of the piston 100. Where multiple rings arepresent, the rings may be designed to perform different or overlappingfunctions. For example, compression rings 102, 104 may be designed toseal the combustion chamber to trap combustion gasses and oil controlrings may be designed to manage engine oil in the cylinder. Spacer rings108 may be provided between two rings 106, 110 to keep the rings spacedapart and is common in oil control ring arrangements. Due to the slidingaction of the piston and piston ring against the cylinder liner wall,reducing the coefficient of friction between the piston ring and wallmay help improve the efficiency of the engine. In combination withexhibiting a relatively low coefficient of friction, it is alsodesirable for piston rings to exhibit high hardness and low wear ratesso as to maintain their integrity over the life cycle of the engine.

The present disclosure is directed to Ti—Si—C—N coated piston rings andmethods of forming such rings. Referring again to FIG. 1, the pistonrings 102, 104, 106, 108, 110 may be split rings with a split 124 thatallows the rings to open and expand for placement over the piston. Whilethe split is illustrated as being a vertical split, the split may assumea number of configurations. The piston rings may be formed from an ironbased alloy, wherein the alloy includes at least 50 atomic percent ofiron. Examples include cast iron, steel, or stainless steel. Inaddition, the rings may exhibit a variety of cross-sectionalconfigurations including barrel face, keystone, torsional, reversetorsional, wiper, or keystone torsional configurations.

The piston rings are coated with Ti—Si—C—N coatings. The Ti—Si—C—Ncoatings may comprise, consist essentially of, or consist of titaniumpresent in the range of 35 to 49 atomic percent, including all valuesand ranges therein, silicon present in the range of 1 to 5 atomicpercent, including all values and ranges therein, carbon present in therange of 17 to 41 atomic percent, including all values and rangestherein, and nitrogen present in the range of 19 to 35 atomic percent,including all values and ranges therein. In embodiments, the coatingsinclude a composition of 43.5 to 46.7 atomic percent titanium, 1.58 to3.04 atomic percent silicon, 30.9 to 34.2 atomic percent nitrogen, and17.6 to 22.5 atomic percent carbon.

In preferred embodiments, the coatings preferably include a compositionof 38 to 48.4 atomic percent titanium, 1.84 to 2.34 atomic percentsilicon, 21.59 to 28.09 atomic percent nitrogen, and 21.5 to 38.1 atomicpercent carbon. In further preferred embodiments, the coatingspreferably include a composition of 35.6 to 43.3 atomic percenttitanium, 2.33 to 4.12 atomic percent silicon, 19.64 to 25.34 atomicpercent nitrogen, and 29.0 to 40.8 atomic percent carbon. In morepreferred embodiments, the coatings preferably include titanium presentin the range of 41 to 43.3 atomic percent, silicon present in the rangeof 2.3 to 3.8 atomic percent, carbon present in the range of 29 to 33atomic percent, and nitrogen present in the range of 22 to 25 atomicpercent.

As noted, the coatings may comprise or consist essentially of theelements of titanium, silicon, carbon and nitrogen at or within theranges noted above or consist of the elements of titanium, silicon,carbon and nitrogen at or within the ranges noted above, with theunderstanding that some amount of impurities may be present depending onthe level of impurities present in the feed stocks or introduced by thedeposition process. For example, the feed stocks or gasses may besupplied containing impurities. Such impurities may be present in therange of 0.001 to 1.0 atomic percent, including all values and rangestherein.

The deposited Ti—Si—C—N coatings may exhibit nanocrystalline phases inan amorphous matrix. The nanocrystalline phases may include TiC_(x)N_(y)phases. In such phases x is in the range of 0.00 to 1.00, including allvalues and ranges therein, such as 0.00, 0.01 to 1.00, 0.01 to 0.10,0.10 to 1.00, etc. and y is in the range of 1.00 to 0.00, including allvalues and ranges therein, such as 0.00, 1.00 to 0.01, 1.00 to 0.10,0.10 to 0.01, etc. In embodiments, TiC_(x)N_(y) phases may include TiN,TiC_(0.3)N_(0.7), TiC_(0.7)N_(0.3), Ti₄N₃, and combinations thereof. Inparticular embodiments, y is equal to 1-x, wherein TiC_(x)N_((1-x)), andphases include TiN, TiC_(0.3)N_(0.7), TiC_(0.7)N_(0.3), etc. Thenanocrystalline phases may exhibit a grain size in the range of 3 nm to10 nm, including all values and ranges therein, such as 4.5 nm to 7 nm.

The amorphous matrix includes a composition selected from diamond likecarbon (DLC), Si—N and Si—C—N, with the understanding that impuritiesmay be present from 0.001 to 1 atomic percent in the amorphous phase,including all values and ranges therein. Again, impurities may beintroduced in the feedstocks or in the deposition process. In particularembodiments, the amorphous matrix may include diamond like carbonincluding varying ratios of sp² bonded and sp³ bonded phases, includingall sp² phases or all sp³ phases.

The coatings may be formed at a thickness of 10 to 40 micrometers,including all values and ranges therein, such as 10 to 20 micrometers.The coatings provide a coefficient of friction of less than 0.15,including all values and ranges therein, such as in the range of 0.05 to0.15, 0.05 to 0.10, etc., as measured on a Plint TE77 testing apparatususing a 10 W-30 oil maintained at 35° C., a normal force of 30 N, and asliding frequency of 5 to 20 Hz. The coatings may also provide acoefficient of friction in the range of less than 0.4, including allvalues and ranges therein such as in the range of 0.16 to 0.4, 0.16 to0.33, 0.21 to 0.33, 0.16 to 0.21, 0.21 to 0.22, as determined via apin-on-disc tribometer using an alumina ball of 0.25 inches in diameterat a load of 1 N at 100 rpm in a dry environment.

The coatings may further provide a nanohardness hardness of 10.0 GPa to30.0 GPa, including all values and ranges therein, such as in the rangeof 10 GPa to 20 GPa, 14.5 GPa to 16.7 GPa, 13.8 GPa to 14.5 GPa, 14.5GPa, etc., as measured by a nanoindenter (NanoIndenter XP™, MTS SystemsCorporation) equipped with a diamond Berkovich indenter by taking 12effective measurements. In addition, the coatings may provide a wearrate of less than 10×10⁻⁶ mm³/N/m, including all values and rangestherein, such as from 3.02×10⁻⁶ mm³/N/m to 7.35×10⁻⁶ mm³/N/m, 4.59×10⁻⁶to 5.025×10⁻⁶ mm³/N/m, 3.84×10⁻⁶ to 5.78×10⁻⁶ mm³/N/m, 4.69×10⁻⁶ mm³/N/mto 5.78×10⁻⁶ mm³/N/m, wherein the wear rate is determined via apin-on-disc tribometer using an alumina ball of 0.25 inches in diameterat a load of 1 N at 100 rpm in a dry environment. The ability of thecoatings, and coated piston rings, to exhibit all three of thesecharacteristics at thicknesses of 40 micrometers or less, andparticularly at a thickness of 20 microns or less, is contemplated toprovide not only improved engine performance in terms of efficiency butalso an increase in engine life span over coatings that exhibit arelatively higher coefficient of friction.

The Ti—Si—C—N coatings may be deposited using physical vapor deposition.In particular, plasma enhanced magnetron sputtering of titanium in thepresence of nitrogen, hexamethyldisilizane, and, optionally, a carboncontaining gas. Generally, plasma enhanced magnetron sputtering mayutilize a gas plasma in the chamber to assist in the coating process,forming denser coatings. In the present process, to introduce silicon,carbon and nitrogen into the coatings, nitrogen gas andhexamethyldisilizane may be supplied to the process chamber during thesputtering process. Acetylene may also be supplied to the processchamber during the sputtering process to increase the carbon content ofthe coatings. In addition to, or alternatively, nitrogen may beintroduced into the process by providing ammonia to the chamber andcarbon may be introduced into the process by providing methane to thechamber.

With reference to FIG. 2, a process chamber 200 may be providedincluding a substrate holder 204 on which substrates (i.e., pistonrings) 202 a, 202 b (referred to herein as substrate 202) may bemounted. While the process chamber may be grounded, a power supply 201may be provided to positively bias the process chamber wall 203 relativeto other components associated with the process chamber, such as anelectron source, work table, substrate or magnetron. Another powersupply 205 may be provided to negatively bias the substrate holder 204,the substrate 202 or both. The power supplies 201, 205 may individuallybe selected as an AC, DC or RF power supply.

A vacuum system 206 may also be provided to reduce the pressure withinthe process chamber. The vacuum system 206 may include an outlet in theprocess chamber 200 that is in fluid communication through a flow pathwith one or more vacuum pumps. In addition, one or more valves may beprovided in the vacuum system 206 to regulate the flow of gasses in thechamber.

The process chamber may further include one or more gas supply ports208. One or more gasses may be provided through each gas supply port208. Gasses provided through the gas supply ports may include argon orother inert gasses such as krypton or xenon. Further process gasses thatmay form a portion of the coating, such as nitrogen or acetylene, mayalso be provided through the gas supply port.

An electron source 210 may also be provided in the process chamber 200.The electron source 210 may include, for example, a hollow cathode, anRF antenna, a microwave generator, a thermionic filament or acombination thereof. As illustrated, the electron source 210 is a singlethermionic filament, which may be formed from tungsten or tantalum. Thefilament may discharge electrons into the system when heated to thethermionic emission temperature of the material forming the filament. Anenergy source 211, i.e., power supply, may be used to apply a bias tothe electron source 210 and may include an AC, DC or RF power supply.

A precursor system may be provided to supply hexamethyldisilizane to theprocess chamber 200. The precursor system may include a vessel 216 forstorage of the hexamethyldisilizane as a liquid and one or more tubes orpipes to provide a flow path 218 between the vessel 216 to the processchamber 200. A mass flow controller 220 may be provided in communicationwith the flow path to regulate the amount of hexamethyldisilizaneentering the process chamber. The vessel 216, flow path 218, and massflow controller 220 may be heated at a temperature in the range of about30° C. to 50° C. using, for example, heater bands, hot air, hot water orhot oil. A liquid flow controller may be used instead of heating thevessel 216. Heating the precursor system, or at least a portion thereof,may volatilize the hexamethyldisilizane so that it may be introduced tothe process chamber 200 in vapor form. The precursor system may alsoinclude a purging system 222 for clearing gasses out of the flow path218 to prevent contamination of the hexamethyldisilizane entering theprocess chamber 200. The purging system may reduce the pressure in theflow path 218 to reduce, or substantially reduce, the presence of gassesin the flow path 218.

The metal (titanium) may be provided by a magnetron. As illustrated,there are two magnetrons 224 a, 224 b (referred to herein as 224)provided in the process chamber. The magnetrons 224 may each include atarget 226 a, 226 b (herein after 226), which provides the metal sourcefor the coatings. The magnetrons may also each include magnets 225 a,225 b (hereinafter 225), which provide a magnetic field in the range of500 Gauss to 1,000 Gauss, including all values and ranges therein. Themagnets may create magnetic fields along the length and surface of eachtarget. A power supply 227 a, 227 b (herein after 227) to bias themagnetron 224 with a negative bias may also be provided.

To coat the piston rings, the piston rings may be provided as asubstrate 202 into the process chamber 200. Once the substrate 202 ispositioned on a work table 204 in the process chamber 200, the gas inthe process chamber 200 may be evacuated and the gas pressure reduced toa pressure in the range of 10⁻⁵ torr to 10⁻⁶ ton, including all valuesand ranges therein, via the vacuum system 206. In embodiments, argon oranother inert gas such as krypton, xenon, etc., may be supplied to thechamber through a gas supply port 208 at a rate of 1 to 200 standardcubic centimeters per minute (sccm), including all values and rangestherein, such as a rate of 5 to 50 sccm. The pressure in the chamber maybe maintained at a range of 1 to 10 millitorrs, including all values andranges therein, using the vacuum system 206. The inert gas may becontinuously fed into the chamber through the duration of the sputteringprocess as well as through the deposition process.

The substrate 202 may optionally be sputter cleaned prior to coating byapplying a bias to the work table 204, the substrate 202, an electronsource 210, chamber wall 203 or a combination thereof. The negative biasapplied to the work table or substrate may be in the range of 20 V to200 Volts including all values and ranges therein, such as in the rangeof 40 V to 100 V. The bias applied to the work table or substrate mayresult in the drawing of ions from the argon gas or global plasma to thesubstrate and sputter cleaning the substrate. Ions may be drawn to thesubstrate or work table at 50 to 300 eV, including all values andincrements therein.

The electron source may be negatively biased in the range of 50 V to 120V, including all values and ranges therein, such as 75 V to 120 Voltsetc. Applying a bias to the electron source 210 may result in electronsbeing ejected into the process chamber 200, causing collisions with theinert gas and separating the gas into ions and electrons, thus formingplasma. In addition, the chamber wall 203 may be positively biased inthe range of 50 to 150 volts, including all values and ranges therein,such as 90 to 100 volts, relative to the filament. In applying a bias tothe chamber wall 203, electrons may be drawn from the electron source210 to the wall surfaces. The electrons may collide with neutral inertgas ions (e.g., argon ions) forming global plasma GP throughout theprocess chamber 200. The sputter cleaning process may occur for 10 to200 minutes, including all values and ranges therein such as in therange of 60 to 90 minutes, removing surface oxides and/or contaminants.

During deposition the flow rate of inert gas into the chamber throughthe gas port 208 may be maintained in the range of 1 to 200 sccm,including all values and ranges therein, such as at a rate of 5 to 50sccm. Nitrogen gas may also be supplied to the process chamber at a flowrate in the range of 40 to 60 sccm, including all values and rangestherein, such as 45 to 50 sccm, through the gas port 208. Inembodiments, a separate gas port may be provided for supplying nitrogen.Acetylene may also be introduced into the process chamber 200. Theacetylene may be introduced through gas port 208 or a separate gas portmay be provided for the acetylene. If introduced, the acetylene may beprovided at a flow rate in the range of 10 to 30 sccm, including allvalues and ranges therein, such as from 15 to 25 sccm, etc.Hexamethyldisilizane may also be introduced into the process chamber 200through the precursor system at a rate in the range of 3 grams per hourto 9 grams per hour of hexamethyldisilizane may be introduced into theprocess chamber 200, including all values and ranges therein, such asfrom 3 to 6 grams per hour.

The biases applied to the substrate, worktable, chamber wall, andelectron source may also be maintained during deposition. The negativebias applied to the work table or substrate may be in the range of 20 Vto 200 V including all values and ranges therein, such as in the rangeof 40 V to 100 V. The electron source may be negatively biased in therange of 50 V to 120 V, including all values and ranges therein, such as75 V to 120 Volts etc. The resulting current to the work table orsubstrate may be in the range of 0.5 A to 20 A, including all values andranges therein. In addition, the chamber wall 203 may be positivelybiased in the range of 50 to 150 volts, including all values and rangestherein, such as 90 to 100 volts, relative to the filament. The bias tothe chamber wall may be developed due to the relative charge of theelectron source and the chamber wall and the energy source 201 may notbe necessary to develop the bias.

The magnetron power supply 227 may negatively bias the magnetron 224 ata range of 0.05 kilowatts to 10 kilowatts, including all values andranges therein, such as from 4 kilowatts to 10 kilowatts. The negativebias applied to the magnetron 224 may draw ions out of gasses proximateto the magnetron 224 forming magnetron plasma P1, P2. Electrons maybecome trapped within the magnetic fields generated by the magnets inthe magnetrons increasing collisions with the gasses near the magnetronsand furthering ionization of the gasses. Due to the negative bias, ionsfrom the magnetron P1, P2 and global plasmas GP may be acceleratedtoward the targets 226 with sufficient energy to remove or sputter atomsfrom the targets 226.

While atoms are sputtered from the magnetron targets, ions from theglobal plasma may bombard the surface of the substrate, including thesputtered atoms of titanium, and produce a protective coating includingthe atoms from the hexamethyldisilizane, nitrogen, and acetylene (ifpresent), on the surfaces of the negatively biased substrate. Thedischarge conditions, i.e., the condition of the global plasma, may beeffective to induce the reactive gas to react with the metal atoms. Thisthen forms the Ti—Si—C—N coatings on the piston ring.

During deposition, the discharge current may be in the range of 1 to 10A, including all values and ranges therein, such as in the range of 4.5to 5.5 A, 5 A, etc. The discharge current may be understood as relatedto the plasma density or ion current. The bias voltage is in the rangeof 30 to 100 V including all values and ranges therein, such as 30 to 50V, 40 V, etc. The bias voltage may be understood as a measure of ionenergy. The bias current may be in the range of 0.50 to 1.00 A,including all values and ranges therein, such as 0.51 to 0.92 A. Thebias current may be understood as a measure of ion flux.

Deposition may proceed from 3 to 10 hours, including all values andranges therein, such as 3 to 5, 3.5 and 4. As noted above, the coatingsmay be formed at a thickness in the range of 10 to 40 micrometers,including all values and ranges therein. The coatings may be relativelyuniform in thickness, wherein the thickness of the coatings may vary+/−20% or less of the average thickness across the coating surface.

In embodiments, prior to depositing the Ti—Si—C—N coatings a bond coatis deposited on the substrate. The bond coat may include titanium,titanium nitride, or a combination thereof. For example, the bond coatmay include one or more alternating layers of titanium and titaniumnitride. In other examples, the bond coat may include one or more layersof titanium nitride phases dispersed in a titanium matrix.

As noted, the deposited Ti—Si—C—N coatings preferably include titaniumpresent in the range of 35 to 49 atomic percent, including all valuesand ranges therein, silicon present in the range of 1 to 5 atomicpercent, including all values and ranges therein, carbon present in therange of 17 to 41 atomic percent, including all values and rangestherein, and nitrogen present in the range of 19 to 35 atomic percent,including all values and ranges therein. These formulations of thecoatings exhibit a remarkable combination of properties, including acoefficient of friction of less than 0.15, a wear rate of less than10×10⁻⁶ mm³/N/m, and a nanohardness in the range of 13.0 GPa to 30.0GPa. The coefficient of friction is measured using the Plint TE77testing apparatus using a 10 W-30 oil maintained at 35° C. as alubricant, a normal force of 30 N, and a sliding frequency of 5 to 20Hz. The wear rate is measured against an alumina ball of 0.25 inches indiameter at a load of 1 N at 100 rpm in a dry environment.

In embodiments, particularly where acetylene is not present in theprocess environment, the coatings preferably include a composition of43.5 to 46.7 atomic percent titanium, 1.58 to 3.04 atomic percentsilicon, 30.9 to 34.2 atomic percent nitrogen, and 17.6 to 22.5 atomicpercent carbon. In such embodiments, the coefficient of friction may bein the range of 0.21 to 0.26 and the wear rate may be in the range of3.02×10⁻⁶ mm³/N/m to 7.35×10⁻⁶ mm³/N/m, wherein the coefficient offriction and wear rate as measured against an alumina ball of 0.25inches in diameter at a load of 1 N at 100 rpm in a dry environment.

In additional embodiments, where acetylene is introduced to the processenvironment in the range of 10 sccm to 30 sccm, the coatings preferablyinclude a composition of 38 to 48.4 atomic percent titanium, 1.84 to2.34 atomic percent silicon, 21.59 to 28.09 atomic percent nitrogen, and21.5 to 38.1 atomic percent carbon. In such embodiments, the Plint TE77coefficient of friction is less than 0.15, including all values andranges therein, such as in the range of 0.05 to 0.10, as measured using10 W-30 oil maintained at 35° C. as a lubricant, using a normal force of30 N applied and a sliding frequency of 5 to 20 Hz. The pin-on-disccoefficient of friction may be in the range of 0.21 to 0.33. The wearrate may be in the range of 4.59×10⁻⁶ mm³/N/m to 5.02×10⁻⁶ mm³/N/m. Thepin-on-disc coefficient of friction and wear rate being measured againstan alumina ball of 0.25 inches in diameter at a load of 1 N at 100 rpmin a dry environment. The nanohardness may be in the range of 14.5 GPato16.7 GPa.

In further embodiments, where acetylene is introduced to the processenvironment in the range of 15 sccm to 25 sccm, the coatings preferablyinclude a composition of 35.6 to 43.3 atomic percent titanium, 2.33 to4.12 atomic percent silicon, 19.64 to 25.34 atomic percent nitrogen, and29.0 to 40.8 atomic percent carbon. In such embodiments, the Plint TE77coefficient of friction is less than 0.15, including all values andranges therein, such as in the range of 0.05 to 0.10, as measured usinga 10 W-30 oil maintained at 35° C. as a lubricant, using a force of 30 Nand a sliding frequency of 5 to 20 Hz. The pin-on-disc coefficient offriction may be in the range of 0.16 to 0.21 and the wear rate may be inthe range of 3.84×10⁻⁶ mm³/N/m to 5.78×10⁻⁶ mm³/N/m, wherein thecoefficient of friction and wear rate as measured against an aluminaball of 0.25 inches in diameter at a load of 1 N at 100 rpm in a dryenvironment. The nanohardness may be in the range of 13.8 GPa to 14.5GPa.

In yet further embodiments, where acetylene is introduced to the processenvironment, such as at a flow rate of 15 to 25 sccm and preferably 18to 22 sccm and more preferably 20 sccm, the coatings preferably includetitanium present in the range of 41 to 43.3 atomic percent, siliconpresent in the range of 2.3 to 3.8 atomic percent, carbon present in therange of 29 to 33 atomic percent, and nitrogen present in the range of22 to 25 atomic percent. In such embodiments, the Plint TE77 coefficientof friction is less than 0.15, including all values and ranges therein,such as in the range of 0.05 to 0.10, as measured using a 10 W-30 oilmaintained at 35° C. as a lubricant, using a normal force of 30 N, and asliding frequency of 5 to 20 Hz. The pin-on-disc coefficient of frictionmay be in the range of 0.21 to 0.22 and the wear rate may be in therange of 4.69×10⁻⁶ mm³/N/m to 5.78×10⁻⁶ mm³/N/m, wherein the coefficientof friction and wear rate as measured against an alumina ball of 0.25inches in diameter at a load of 1 N at 100 rpm in a dry environment. Thenanohardness may be in the range of 10 to 20 GPa, including all valuesand ranges therein, and preferably 14.5 GPa.

EXAMPLES Samples

Stainless steel (SS) disc coupon samples (1 inch×1 inch×⅛ inch) andsteel keystone 137 mm bore piston rings were used in the examplesherein. The coupons were used for the coating microstructural analysesand pin-on-disc wear tests, while the rings were tested in the PlintTE77 apparatus and single cylinder engine test.

Coating Process

Ti—Si—C—N coatings were formed using the process parameters describedbelow in Table 1. Prior to coating deposition, each sample substrate wascleaned by etching with inert ions using a global plasma at a biasvoltage of −120 V. The voltage and current applied on the filamentsduring sputter cleaning were 20 V and 40 A. After ion etching, a Ti/TiNbond layer was deposited to enhance the adhesion strength of thecoatings.

To form the coating two titanium targets were used in DC magnetronsputtering at a 4 kW average power (MDX, 10 kW, Advanced Energy, Inc.)positioned in the process chamber. Argon, nitrogen, hexamethyldisilizane(HMDSN) and acetylene (C₂H₂) gasses were supplied in the processchamber. Tungsten filaments were used as an electron source. Argon flowrate was maintained at 190 sccm. The chamber pressure was maintained atabout 3 m Ton in all samples and trials. Coatings having a thickness inthe range of 12 to 15 microns were deposited for a deposition period of3 hours.

TABLE 1 Processing Parameters 1^(st) 2^(nd) Deposit Target TargetDischarge Bias Bias Flow Rate Flow Rate Flow Rate Time Power PowerCurrent Voltage Current N₂ HMDSN C₂H₂ Sample (hr) (kW) (kW) (A) (V) (A)(sccm) (g/hr) (sccm) 1 3 4 4 5 40 0.66 50 3 2 4 4 4 5 40 0.65 50 6 3 5 44 5 40 0.92 50 12 4 5 4 4 5 40 0.82 50 15 5 3.5 4 4 5 40 0.85 50 18 6 34 4 5 40 0.51 50 1.5 7 3 4 4 5 40 0.57 45 3 8 3 4 4 5 40 0.67 45 3 5 9 34 4 5 40 0.58 45 3 10 10 3 4 4 5 40 0.6 45 3 15 11 3 4 4 5 40 0.54 45 320 12 3 4 4 5 40 0.58 45 3 30 13 3 4 4 5 40 0.54 45 3 40 14 3 4 4 5 400.57 45 3 50 15 3 4 4 5 40 0.54 45 3 17.5 16 3 4 4 5 40 0.54 45 3 20 173 4 4 5 40 0.54 45 3 22.5 18 3 4 4 5 40 0.54 45 3 25

Three groups of coatings were deposited. In the first group, samples1-7, the flow rate of hexamethyldisilizane (HMDSN) was varied, while noacetylene (C₂H₂) was introduced. In the second group, samples 8-14, theflow rate of acetylene (C₂H₂) was varied from 5 to 50 sccm while theflow rate of hexamethyldisilizane was maintained at 3 g/hr. In the thirdgroup, samples 15-18, the flow rate of acetylene (C₂H₂) was varied from17.5 to 25 sccm while the flow rate of hexamethyldisilizane wasmaintained at 3 g/hr. The flow rate of nitrogen (N₂) was maintained at50 sccm for samples 1 through 6 and 45 sccm for samples 7 through 18.

Experimental Procedures

Scanning electron microscopy (SEM) using a Philips XL 40 scanningelectron microscope was used to study the coating microstructure andmorphology. Cross-sections were examined using SEM to determine coatingthickness. In addition, energy dispersive spectroscopy (EDS) was used toperform elemental analysis. X-ray diffractions were generated using aSiemens Kristalloflex 805 diffractometer using Cu radiation (45 kV and30 mA) in Bragg-Brentano mode.

Rockwell C indentation at 150 kg load was performed on the coatings andthen studied using SEM. Nanoindentation was also performed on selectedsamples to study the coating nanohardness and modulus of elasticity. Themean hardness and Young's modulus of the Ti—Si—C—N coatings weremeasured using a nanoindenter (NanoIndenter XP™, MTS SystemsCorporation) with a diamond Berkovich tip. The indentation depth was 300nm, which was less than 10% of the thickness of the coating to avoid theeffect from the substrate deformation. The hardness (H) and Young'smodulus (E) of the coating were calculated by the nanoindenter software(TestWorks™ Ver.4.06A) based on the model of Oliver and Phan from theload-displacement curves. Twelve measurements were made to obtain themean value and the standard deviation.

The adhesion of the coatings was measured by the Rockwell-C indentationtest (RC) using a standard Rockwell-C hardness tester. A Rockwell Cdiamond stylus (cone apex angle 120°, tip radius R=0.2 mm) was used toperform the tests with an applied load of 150 kg on the stylus. Afterthe tests, the morphology of the indentations was examined using SEM toevaluate coating damage around the indents. The damage of the coatingwas compared with a HF adhesion strength quality as standardized in theVDI guidelines 3198, (1991).

Coating tribology was measured using a pin-on-disc tribometer, aschematic of which is illustrated in FIG. 3. This test was performed onthe stainless steel disc coupons for screening purposes. The counter pinused was an alumina ball of 6 mm in diameter and the applied load F was1 N, and the rotating speed was 100 rpm. The testing occurred in anon-lubricated environment for 10,000 cycles.

A few of the coated rings were also tested using the Plint TE77 testingapparatus, which was performed using diesel engine oil as a lubricant.The oil was Shell ROTELLA, which is 10w-30 oil, and had been drainedfrom a prototype high efficiency heavy duty diesel engine. This oil wasused to provide stable friction measurements. During testing, the oiltemperature was maintained at 35° C. to provide the desired viscosity.FIG. 4a illustrates a schematic of the test, wherein a sample is slideback and forth FS against a sliding surface at a given frequency under anormal force F1, which is applied normal to the sliding surface. FIG. 4billustrates the testing points, wherein the test was performed atfrequencies of 5 Hz, 10 Hz, 15 Hz and 20 Hz and normal forces of 15 N,30 N and 45 N.

After Plint TE77 testing the deposition parameters were selected and afew rings were selected and tested in a single cylinder Ricardo Hydragasoline engine shown in FIG. 5. The test was conducted using thefollowing parameters: 0.5 L displacement, 86 mm piston, 86 mm stroke,and 10.5:1 compression ratio. The valve train is characterized as adirect-acting lifter design, twin overhead cam. Operating parameters ofthe engine include: 5 w20 fully formulated engine oil, 100° C. enginecoolant in and out temperature, 250 kPa engine oil pressure, 65° C.engine oil gallery temperature, and 2000 rpm reciprocation. The enginewas run over a 24 hour period using a combination of motoring and firingat steady and increasing speeds and loads.

Heavy duty diesel engine testing was then performed using piston ringscoated according to sample 11 for the top and second compression rings(rings 102, 104 illustrated in FIG. 1). The engine chosen was a singlecylinder oil test engine as shown in FIG. 6 using one cylinder from aCaterpillar 15 L engine. The engine had a 137 mm bore, articulated steelpiston with aluminum skirt, and keystone top ring. The engine wasoperated at a peak torque for 120 hours of continuous testing. Peaktorque (approximately 385 Nm) occurs at 1200 RPM. An oil drain fromanother engine which contained 4.1% soot by mass was used to acceleratethe wear process. This test was operated with an engine oil temperatureof 125° C. and oil gallery pressure of 350 kPa. During testing aninductively coupled plasma (ICP) analysis was performed to check forwear materials every 12 hours, providing an indicator of wear rate fordifferent parameters such as the coating and base metal.

Results and Discussion Coating Properties and Elemental Composition

Tables 2 and 3 provide the experimental results indicating theproperties of the coatings and elemental coating composition.

TABLE 2 Coating Properties Flow Rate Flow Rate Deposition Wear RateNano- Modulus HMDSN C₂H₂ Thickness Rate COF (pin- (×10⁻⁶ HardnessElasticity Sample (g/hr) (sccm) (μm) (μm/hr) on- disc) mm³/N/m) (GPa)(GPa) 1 3 0.25 5.1 29.4 350 2 6 0.26 3.02 25.8 305 3 12 20.1 4.02 0.414.6 21.5 311 4 15 19.6 3.92 0.7 17.8 20.6 302 5 18 13.1 3.74 0.9 25.68.3 149 6 1.5 17.5 5.83 0.93 36.1 27.6 334 7 3 11.1 3.70 0.21 7.35 8 3 520 6.67 0.55 4.33 21 295 9 3 10 16.5 5.50 0.33 4.59 16.7 255 10 3 1513.5 4.50 0.24 5.02 11 3 20 14.4 4.80 0.22 4.69 14.5 183 12 3 30 16.55.50 0.21 4.71 13 3 40 10.1 3.37 0.19 2.96 13.4 133 14 3 50 19.5 6.500.16 12.3 15 3 17.5 16.6 5.53 0.18 4.59 16 3 20 16.1 5.37 0.21 5.78 17 322.5 16.2 5.40 0.19 4.59 18 3 25 17.4 5.80 0.19 3.84 13.8 138

TABLE 3 Elemental Compositions of the Coatings Flow Rate Flow Rate HMDSNC₂H₂ C N Si Ti Sample (g/hr) (sccm) (at %) (at %) (at %) (at %) 1 3 2 622.5 30.98 3.04 43.5 3 12 20 32.76 4.22 43 4 15 19.5 31.84 5.04 43.6 518 22 28.44 6.46 43.1 6 1.5 17.6 35.59 1.1 45.7 7 3 17.6 34.2 1.58 46.78 3 5 20.8 27.89 1.28 50 9 3 10 21.5 28.09 2.05 48.4 10 3 15 24 27.511.84 46.6 11 3 20 29 25.34 2.33 43.3 12 3 30 38.1 21.59 2.34 38 13 3 4046.7 17.48 2.42 33.4 14 3 50 55.2 15.97 1.96 26.9 15 3 17.5 30.4 23.573.77 42.3 16 3 20 32.8 22.29 3.83 41.1 17 3 22.5 36.3 20.6 4.12 39 18 325 40.8 19.64 3.91 35.6

The nanohardness and modulus of samples 1 through 7 are graphed in FIG.7 relative to the flow rate of the hexamethyldisilizane. As can be seenin the graph, both hardness and modulus reach a maximum at 3 g/hr. Asillustrated in FIG. 8 the coefficient of friction and wear rate obtainedusing pin-on-disk tribology is graphed relative to the flow rate of thehexamethyldisilizane. As can be seen in the graph, the coefficient offriction is lowest when the hexamethyldisilizane flow rate is at 3 gramsper hour and remains below 0.4 at flow rates between 3 grams per hourand 12 grams per hour. Similarly, the wear rate is lowest when thehexamethyldisilizane flow rate is in the range of 3 grams per hour and 6grams per hour, remaining below 5×10⁻⁶ mm³/N/m. Based on the data, itappears that at a flow rate of hexamethyldisilizane in the range of 3grams per hour and 9 grams per hour the coefficient of friction remainsbelow 0.4 and the wear rate remains below 10×10⁻⁶ mm³/N/m.

As a flow rate of 3 grams per hour of hexamethyldisilizane providedbetter properties overall, the hexamethyldisilizane flow rate wasmaintained at 3 grams per hour while acetylene was introduced into thesystem at varying flow rates in samples 8 through 14. FIG. 9 illustratesthe effect of acetylene flow rate on the coefficient of friction and thewear rate. As can be seen, in FIG. 9, the coefficient of friction isbelow 0.4 at acetylene flow rates of 10 sccm or greater. However, thewear rate increases at an acetylene flow rate of 50 sccm to greater than12×10⁻⁶ mm³/N/m. At 40 sccm and below, the wear rate remains below about5×10⁻⁶ mm³/N/m. In view of this data, it appears that acetylene may beintroduced at a flow rate in the range of 10 sccm to 40 sccm, includingall values and ranges therein.

The coefficient of friction using the Plint TE77 test was also measuredfor samples 8, 11, 12 and 13 and the results are presented in FIG. 10.As seen in this figure, the coefficient of friction was lower when theflow rate of acetylene was in the range of 10 to 30 sccm. At theserates, the coefficients of friction were similar, and lower at higherfrequencies, than that of the baseline of cast iron as seen in FIG. 10.Using flow rates of 5 sccm and 40 sccm resulted in a relatively highercoefficient of friction and a relatively higher wear rate, respectively.

In view of the above, the acetylene flow rate was varied at finer stepsfrom 17.5 to 25 sccm. Note that sample 16 is a repeat of sample 11. FIG.11 illustrates the results of Plint TE77 testing. The performance of thecoatings appears to be similar and, at most frequencies, below that ofthe cast iron baseline material seen in the graph. Specifically, itappears that at 10 Hz, the coefficient of friction was below 0.09 forthe samples tested, whereas the coefficient of friction was above 0.09for cast iron. Similarly at 15 Hz, the coefficient of friction of thesamples appeared to be below 0.08, whereas the coefficient of frictionof the cast iron appears to be 0.08. At 20 Hz, the coefficient offriction of the samples appears to be 0.065 or below, whereas thecoefficient of friction of the cast iron is above 0.065.

FIG. 12 illustrates the coefficient of friction as measured by the PlintTE77 test for varying amounts of hexamethyldisilizane in samples formedwithout acetylene present in the process chamber, samples 3, 4 and 5. Asseen in FIG. 12, the coefficient of friction of these samples wasrelatively higher than that of the cast iron. Note that these sampleswere tested at a normal force of 15 N whereas all previous samples inFIGS. 10 and 11 were tested at 30 N.

With regard to the elemental compositions produced by the coatingmethods, FIG. 13a illustrates the effect of HMDSN flow rate on thecoating composition for samples 2 through 6 and 7. The amount oftitanium was highest at 3 g/hr and the silicon content increasedrelatively linearly with increasing hexamethyldisilizane flow rate waskept the same. The highlighted area illustrates the flow rate where theproperties were relatively better overall. FIG. 13b presents the XRDpatterns of the Ti—Si—C—N coatings deposited with different HMDSN flowrates. All Ti—Si—C—N coatings exhibited polycrystalline structure. Thecoating deposited at a HMDSN flow rate of 1.5 g/hr exhibited a facecenter cubic (FCC) phase structure with (111), (200), (220) diffractionpeaks. The (200) diffraction peaks showed the highest intensity. As theHMDSN flow was increased to 3 and 6 g/hr, the intensity of the (200)peak decreased with a peak broadening for all diffraction peaks. Inaddition, the diffraction peaks for the Ti adhesion layer and the steelsubstrate were also shown in the XRD patterns. Since the thickness ofthe coatings is similar, the appearance of the Ti diffraction peaks inthe XRD patterns indicated an increase in the amorphous phase in theTi—Si—C—N coatings as the HMDSN flow rate increased, as X-ray has a deeppenetration depth in amorphous phases.

FIGS. 14a and 14b illustrate the effect of acetylene flow rate on thecoating composition for samples 8 through 14. As seen in FIG. 14a , theconcentration of C increases with increasing acetylene flow rate.Further, the concentrations of Ti and N decrease and Si remains fairlyconsistent as the acetylene flow rate increased. The highlighted areaillustrates the flow rate where the properties were relatively betteroverall. FIG. 14b presents the XRD patterns. These coatings alsoexhibited an FCC phase structure with (111), (200) and (220) diffractionpeaks. As the acetylene flow was increased, the intensity of the (200)peak decreased accompanied with an increase in the (111) peak. Thediffraction peaks for the titanium adhesion layer and the steelsubstrate increased significantly as the acetylene flow rate wasincrease, which is related to an increase in the amorphous carbon phasein the coatings.

SEM Imaging

FIGS. 15a, 15b and 15c illustrate SEM images of samples 3, 4 and 5produced using hexamethyldisilizane without acetylene. In each figure,sample 3 is at the top, sample 4 is in the middle, and sample 5 is atthe bottom of the images. FIG. 15a include images of Rockwell C (RC)indentation on the coating surfaces, FIG. 15b includes images of thecoating surfaces without indentation, and FIG. 15c includes images ofcross-sectional views of the coatings. Overall, the coatings includemany droplets on the surface. In addition, the coatings exhibit columnarstructure. Further, at a high hexamethyldisilizane flow rate, thecoating becomes coarse. Finally, delamination is not observed around theRC indents indicating adhesion is relatively good.

FIGS. 16a, 16b, and 16c illustrate SEM images of samples 8, 11, 12 and13, wherein sample 8 is at the top, sample 11 is at the top middle,sample 12 is at the bottom middle, and sample 13 is at the bottom of theimages. FIG. 16a includes images of RC indentation on the coatingsurfaces, FIG. 16b includes images of the coating surfaces withoutindentation, and FIG. 16c includes images of cross-sectional views ofthe coatings. It is noted that as the amount of acetylene increases, thedroplets and columnar structure decreases. In addition, the surfacemorphological features become smaller as acetylene flow rate increases.Finally, the coatings become more brittle as acetylene flow rateincrease. Based on industry criteria, VDI 3198 (Verein DeutscherIngenieure Normen, VDI 3198, VDI-Verlag, Dusseldorf, 1991), the coatingadhesion for sample 8 was the best. Samples 11 and 12 are acceptable.However, sample 13 is unacceptable.

FIGS. 17a, 17b and 17c illustrate SEM images of samples 15, 16 and 17,wherein sample 15 is at the top of the images, 16 is in the middle and17 in at the bottom. FIG. 17a includes images of RC indentation on thecoating surfaces. FIG. 17b includes images of the coating surfaces. FIG.17c includes images of cross-sectional views of the coatings. Thestructure, morphology and indentation appear to be similar. Few dropletson the coating surfaces are observed. The columnar structure seen insamples 3, 4, and 5 is not seen and delamination is not observed,indicating that adhesion is relatively good.

In addition, it can be seen from FIGS. 18a and 18b that the coatingshave a nanocomposite structure. The coating imaged containsnanocrystalline phases with nanocrystalline grain sizes that fall in therange of 3 to 10 nm, which may be attributed to the TiCN crystallinephases. The amorphous phase was found to be mainly composed of Si—C—N.FIG. 18b includes a selected area electron diffraction (SAED) pattern ofthe coating which confirms the coating has a polycrystalline face centercubic (FCC) phase which may be attributed to the TiCN.

Friction Test

A set of piston rings were produced including the top, second and oilcontrol ring, by coating rings using the depositions parameters used inSamples 11 and 16 described above. This set of rings was installed onthe friction engine. The engine was run over an 8 hour period using acombination of motoring and firing at steadily increasing speeds (1500,2000, 2500, 3000 and 2500 rpm) and loads (40,60 and 75% engine load).The ring wear was measured using optical profilometry and the wear depthwas barely measurable at less than 1 micron. FIG. 19a is a photograph ofthe coated rings on the piston and FIG. 19b is a 3D microscope image ofthe top ring. FIG. 19c is a profile taken in the x-direction using the3D microscope and FIG. 19d is a profile taken in the y-direction usingthe 3D microscope after running in the engine for 24 hours.

The coefficient of friction contribution from the coated rings in thesingle cylinder engine was obtained using the difference between themaximum amount of work the engine can do and the actual amount of workthe engine actually did. The in-cylinder pressure data is used todetermine the maximum amount of work the engine can do. The actualamount of work performed is calculated form the output torque. Thedifference is caused by engine inefficiencies, including those due tofriction loss (total friction work). The total friction loss includesthe work loss due to friction in the piston, valve train, bearings, oilseals, pumps including oil, water and fuel pumps, alternator, andpumping losses. The contribution of the piston ring coefficient offriction to the total friction loss may be estimated from a comparisonof the piston assembly friction with the total friction loss (which isdependent on the power output of the engine).

FIG. 20 is a graph of the absolute magnitude of the friction in oneengine cycle for coated and uncoated piston rings. After normalization,it can be calculated that the coated piston ring contributes to 18% ofthe total coefficient in the friction engine test. In contrast, theuncoated piston rings contribute to 25% to 34% of the total coefficientof friction in two different tests.

Durability Test

Based on the results of the friction engine test a coating was appliedto the top and second ring of the single cylinder oil test engine usingthe conditions of sample 11. The test results showed lower ring weightloss for both the coated top and second ring. In addition, the matingsurfaces of the cylinder liner demonstrated lower wear as indicated by a12 point wear step measurement wherein wear is measured at 12circumferential points around the liner of the piston seen in FIG. 21a .The results of the liner wear step measurements are shown in FIG. 21b .Although both tests showed wear steps that are on the low end of what istypically measured, the coated test still showed a 78% reduction inaverage liner wear, as seen in FIG. 21 c.

FIGS. 22a and 22b illustrate the amount of iron and titanium present inengine oil over a period of 120 hours for the cast iron baselinematerial and the coated ring as measured using inductively coupledplasma analysis. As seen in FIG. 22a , the test results indicate thatiron concentrations for the coated and baseline materials was similarand indicates normal overall engine wear for both cases. FIG. 22billustrates a steady accumulation of titanium in the engine oil, whichsuggests a steady wear rate for the coating throughout the entire testperiod as the only source for the titanium was the Ti—Si—C—N coating.

Deposition Rates

The coating deposition rate may be found in Table 2 reproduced above.Generally, the deposition rate is in the range of 3.3 to 6.7 micrometersper hour. Where the reactive gas flow rate of N₂ and HMDSN are 45 sccmand 3 g/h, respectively, and the flow rate of C₂H₂ in the range of 10 to25 sccm, the deposition rate is between 4.5 and 5.8 micrometers perhour. The rate of deposition is much higher than most CrN coating rates.Consequently, the deposition of the Ti—Si—C—N coatings herein may besuperior to the commercially used CrN production coatings.

The foregoing description of several methods and embodiments has beenpresented for purposes of illustration. It is not intended to beexhaustive or to limit the claims to the precise steps and/or formsdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be defined by the claims appended hereto.

What is claimed is:
 1. A method of coating piston rings, comprising:placing a piston ring into a process chamber; reducing gas pressure insaid process chamber; supplying an inert gas to said process chamber andgenerating a plasma of said inert gas; supplying nitrogen to saidprocess chamber at a flow rate of 40 sccm to 60 sccm; supplyinghexamethyldisilazane to said process chamber at a rate of 3 grams perhour to 9 grams per hour; sputtering titanium from a magnetron target insaid process chamber; and depositing a Ti—Si—C—N coating on said pistonring, wherein said coating has a thickness in the range of 10.0micrometers to 40.0 micrometers and exhibits a coefficient of frictionof less than 0.15, a wear rate of less than 10×10⁻⁶ mm³/N/m, and ananohardness in the range of 10.0 GPa to 30.0 GPa, wherein saidcoefficient of friction is measured using a Plint TE77 testing apparatususing 10 W-30 oil maintained at 35° C. as a lubricant, under a force of30 N, and a sliding frequency of 5 to 20 Hz, and said wear rate ismeasured against an alumina ball of 0.25 inches in diameter at a load of1 N at 100 rpm in a dry environment, wherein said Ti—Si—C—N coatingincludes nanocrystalline phases having a grain size in the range of 3 nmto 10 nm in an amorphous matrix, wherein said nanocrystalline phasesinclude TiC_(x)N_(y), wherein x is in the range of 0.00 to 1.00 and y isin the range of 1.00 to 0.00.
 2. The method of claim 1, wherein saidnitrogen is supplied to said process chamber as nitrogen gas, ammonia,or combinations thereof.
 3. The method of claim 1, further comprisingsupplying carbon to said process chamber, wherein said carbon issupplied as acetylene, methane, or combinations thereof.
 4. The methodof claim 1, further comprising negatively biasing an electron source inthe range of 50 V to 120 V to form said plasma and said process chamberis biased in the range of 50 V to 150 V relative to said electronsource.
 5. The method of claim 1, wherein said piston ring is negativelybiased in the range of 20 V to 200 V and said magnetron is negativelybiased in the range of 0.05 to 10 kW.
 6. The method of claim 1, whereinsaid deposited coating comprises titanium present in the range of 35 to49 atomic percent, silicon present in the range of 1 to 5 atomicpercent, carbon present in the range of 17 to 41 atomic percent, andnitrogen present in the range of 19 to 35 atomic percent.
 7. The methodof claim 1, wherein said deposited coating comprises titanium present inthe range of 43.5 to 46.7 atomic percent, silicon present in the rangeof 1.58 to 3.04 atomic percent, carbon present in the range of 17.6 to22.5 atomic percent, and nitrogen present in the range of 30.9 to 34.2atomic percent.
 8. The method of claim 7, wherein the coefficient offriction is in the range of 0.21 to 0.26, and the wear rate is in therange of 3.02 to 7.35×10⁻⁶ mm³/N/m.
 9. The method of claim 1, furthercomprising supplying acetylene to said process chamber at a flow rate inthe range of 10 sccm to 30 sccm and said deposited coating comprisestitanium present in the range of 38 to 48.4 atomic percent, siliconpresent in the range of 1.84 to 2.34 atomic percent, carbon present inthe range of 21.5 to 38.1 atomic percent, and nitrogen present in therange of 21.59 to 28.09 atomic percent.
 10. The method of claim 9,wherein the coefficient of friction is in the range of 0.21 to 0.33, thewear rate may be in the range of 4.59×10⁻⁶ mm³/N/m to 5.02×10⁻⁶ mm³/N/m,and the nanohardness may be in the range of 14.5 GPa to16.7 GPa.
 11. Themethod of claim 1, further comprising supplying acetylene to saidprocess chamber at a flow rate in the range of 15 sccm to 25 sccm andsaid deposited coating comprises titanium present in the range of 35.6to 43.3 atomic percent, silicon present in the range of 2.33 to 4.12atomic percent, carbon present in the range of 29.0 to 40.8 atomicpercent, and nitrogen present in the range of 19.64 to 25.34 atomicpercent.
 12. The method of claim 11, wherein the coefficient of frictionis in the range of 0.16 to 0.21, the wear rate is in the range of3.84×10⁻⁶ mm³/N/m to 5.78×10⁻⁶ mm³/N/m, the nanohardness is in the rangeof 13.8 GPa to 14.5 GPa.
 13. The method of claim 1, further comprisingsupplying acetylene to said process chamber wherein said depositedcoating comprises titanium present in the range of 41 to 43.3 atomicpercent, silicon present in the range of 2.3 to 3.8 atomic percent,carbon present in the range of 29 to 33 atomic percent, and nitrogenpresent in the range of 22 to 25 atomic percent.
 14. The method of claim13, wherein the coefficient of friction may be in the range of 0.21 to0.22 and the wear rate is in the range of 4.69×10⁻⁶ mm³/N/m to 5.78×10⁻⁶mm³/N/m.
 15. The method of claim 1, wherein said amorphous matrixincludes one of the following compositions: diamond like carbon, Si—N,and Si—N—C.
 16. (canceled)
 17. (canceled)
 18. (canceled)
 19. (canceled)20. (canceled)
 21. (canceled)
 22. (canceled)
 23. (canceled) 24.(canceled)